1. Field of the Invention
The present invention relates to an output circuit for an electronic display device driver, and more specifically to an output circuit of a CMOS structure used in a common driver for a flat panel electronic display device such as a liquid crystal display, an electroluminescent display, a plasma display panel, and the like.
2. Description of Related Art
Conventionally, a flat panel electronic display device driver of a matrix electrode structure includes a number of row (or scanning) electrodes formed on a first substrate and a number of column (or signal) electrodes formed on a second substrate orthogonally to the row electrodes. A voltage is applied to selected ones of intersections (pixels) between the row electrodes and the column electrodes, so that a character display, a graphic display or a movie display is effected.
The row electrodes are associated with a common driver, so that in an ordinary operation, the row electrodes are sequentially scanned by the common driver in a line sequential scanning manner. When the display panel is to be reset, all of the row electrodes are forcibly brought into a "H" (high logical) level or into a "L" (low logical) level. The output circuit used in the common driver for the flat panel electronic display device has the above mentioned function. In the following, the output circuit used in the common driver for the flat panel electronic display device will be sometimes called simply an "output circuit".
A typical output circuit used in the common driver for the flat panel electronic display device includes "n" 2-input OR circuits where "n" is a positive integer and corresponds to the number of the row electrodes of the display panel. One input of each of the OR circuits is connected to receive a control signal from an external of the output circuit. The other input of the OR circuits is connected to receive a corresponding bit of an n-bit shift register, and an output of the OR circuits is connected to a corresponding one of the row electrodes of the display panel so as to drive the corresponding electrode.
In this conventional output circuit, when the display panel performs an ordinary display operation, the control signal is maintained at the "L" level, an output signal of each stage of the shift register is outputted, as it is, from the associated OR circuit, so that the row electrodes of the display panel are sequentially scanned. On the other hand, at the time of resetting the display panel, the control signal is brought to the "H" level, so that the output signal of all the OR circuits are brought to the "H" level at once, regardless of the output signal of the respective stages of the shift register.
As mentioned above, when all the output signals of the output circuit are brought into the "H" level (or in the "L" level in the case of a negative logic) in accordance with the control signal, all the output signals are simultaneously brought into the "H" level. Therefore, in case that the output circuit is formed of a CMOS (complementary metal-oxide-semiconductor transistor) circuit, when the output signals are switched over, a pass-through current of the amount in proportion to the number of the output signals flows. In other words, a large voltage supply current flows transiently.
In the case that the common driver including the above mentioned output circuit is formed in an integrated circuit, if the above mentioned large current flows in the voltage supply, a latch-up phenomenon often occurs, or a noise is superimposed on signal conductors, or the voltage supply-voltage becomes unstable. As a result, the integrated circuit becomes easy to malfunction.